Assembly by mechanical connection including at least one part made of composite material

ABSTRACT

An assembly includes a first part made of composite material and a second part, which parts are held one against the other by at least one fastener system having a fastener element with a head from which there extends a shank. The fastener system further includes a bushing, the bushing including a collar presenting an inside face and an outside face of conical shape. The head of the fastener element bears against the inside face of the collar, while the outside face of the collar bears against a countersink formed in the first part.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/745,256, filed Jan. 16, 2018, which is the U.S. National Stage ofPCT/FR2016/051822 filed Jul. 15, 2016, which in turn claims priority toFrench Application No. 1556776 filed Jul. 17, 2015. The contents of allapplications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The invention relates to using mechanical connection to assembletogether parts made of thermostructural composite material, such as aceramic matrix composite (CMC) material or a carbon-carbon (C/C)material, which material is typically made up of a porous substrate suchas a porous fiber substrate, that is densified with a matrix. The fibersof the substrate may in particular be carbon fibers or ceramic fibers.The matrix is a refractory ceramic, such as for example: a carbide, anoxide, a nitride, a boride, or a refractory oxide. Thermostructuralcomposite materials are remarkable for their mechanical properties,which make them suitable for constituting structural elements, and fortheir ability to retain those properties at high temperatures.

The invention relates more particularly to the mechanical and thermalbehavior of mechanical connections used for assembling together partsmade of thermostructural composite material when those parts are to beimmersed in high temperature streams, as applies for example whenfabricating all or some of the afterbody assemblies of an aeroenginesuch as exhaust cones (also known as “plugs”) or flaps forvariable-section nozzles, or indeed any other hot fairing such as theaft fairing on a pylon for attaching an engine to an aircraft, known asthe aft pylon fairing (APF).

In such applications, the parts that are to be assembled together aregenerally relatively fine (thickness of a few millimeters) and they needto satisfy aerodynamic requirements, which makes it preferable to usefastener elements of the plane surface or “flush” type in order to makemechanical connections between the parts. For assemblies that are usedto make afterbody portions of an aeroengine, it is general practice touse fastener elements that present a flat head at one end of thefastening, which head is received in a countersink formed in one of theparts to be assembled together, and a spacer or a washer at the otherend for enabling differential expansion to be taken up between thefastener elements, which expand significantly, and the parts made ofthermostructural composite material, which expand less. Incorporatingthe head of the fastener element flush in a countersink present at oneend of the fastening serves to obtain good aerodynamic performance.Nevertheless, the pre-loading or tightening force that is applied to theconnection by the fastener element needs to be limited in order toensure that the parts for assembling together and that are made out ofcomposite material are not damaged by crushing and/or shear.

OBJECT AND SUMMARY OF THE INVENTION

An object of the invention is to propose a solution for assembling atleast one part made out of composite material by using one or morefastener systems that present a coefficient of thermal expansion that isgreater than the coefficient of thermal expansion of the part(s) made ofcomposite material, with the fastener system being capable of enabling ahigh pre-loading or tightening force to be used without impacting themechanical performance of the assembly, thereby improving its capacityfor connection.

This object is achieved with an assembly comprising a first part made ofcomposite material and a second part, which parts are held one againstthe other by at least one fastener system having a fastener element witha head from which there extends a shank, the fastener system also havinga bushing, said bushing including a collar presenting an inside face andan outside face of conical shape, the head of the fastener elementbearing against the inside face of the collar, while the outside face ofthe collar bears against a countersink formed in the first part, theassembly being characterized in that the fastener system comprises ascrew having a flat head from which there extends a shank provided witha threaded portion and a nut having tapping co-operating with thethreaded portion of the screw, the collar presenting an inside face ofconical shape that receives the flat head of the screw, the outside faceof the collar presenting a cone angle greater than the cone angle of theinside face of said collar.

Thus, by using a bushing with its collar having an outside facepresenting a conical shape and extending over a diameter greater thanthe width or the diameter of the head of the fastener element, thebearing area of the head of the fastener element against the compositematerial part is increased. This increase in bearing area serves toreduce the crushing pressure and the inter-lamination shear stress inthe part, thereby making it possible to increase the tightening forcebetween the parts without the risk of damage, thus increasing thecapacity of the connection to take up force. In addition, the fastenersystem is designed to apply a continuous holding force by radialexpansion, thereby serving to compensate for the expansion of eachfastener system, in particular its axial expansion, and to conserve atightening force when hot.

The assembly of the invention is made using mechanical connections thatare flush with one side of the assembly, i.e. they do not project beyondthe outside surface of one of the assembled-together parts.

Consequently, the assembly of the invention may be immersed on one sidein a high temperature stream without aerodynamic performance beingdegraded as a result of the connection systems.

Since the screw-bushing interface is decoupled from the interface withthe part, it is possible to use screws that are standard, i.e. easy andinexpensive to obtain, since the cone angle presented by the inside faceof the collar of the bushing can be matched to the cone angle ofstandard screws without impact on the connection.

In another embodiment of an assembly in accordance with the invention,the fastener system comprises a rivet having a flat head from whichthere extends a shank having an enlarged end and a first washerincluding a central countersink against the surface of which theenlarged end of the shank of the rivet rests, the outside face of thecollar presenting a cone angle that is greater than the cone angle ofthe inside face of said collar.

In an aspect of the assembly of the invention, the fastener systemfurther comprises a washer interposed between the facing faces of thefirst and second parts for assembling together. The washer makes itpossible to leave a space between the parts for assembling together inorder to control the contact zone in terms of shape, size, and surfacestate of the contact between the parts. The washer may also have afunction of compensating the connection tightening by using anappropriate material for the washer.

In another aspect of the invention, the fastener system furthercomprises a spacer interposed between the second assembled part and thenut when the fastener system has a screw, or between the second part andthe first washer when the fastener system has a rivet, thereby enablingforces to transit between the nut or the first washer and the part whilereducing any discontinuities of section modulus. The spacer preferablypresents a coefficient of thermal expansion that is greater than thecoefficient of thermal expansion of the screw or the rivet in order tomaintain the tightening force applied by the connection at alltemperature levels.

In another aspect of the assembly of the invention, the second part ismade of metal or of composite material.

In yet another aspect of the assembly of the invention, each of thefirst and second parts presents a thickness of less than 3 millimeters(mm).

In still another aspect of the assembly of the invention, the first andsecond parts are aeroengine afterbody parts or aerodynamic fairing partsof an aft pylon fairing.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention appear from thefollowing description of particular embodiments of the invention givenas non-limiting examples and made with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic perspective view showing an assembly made inaccordance with an embodiment of the invention;

FIG. 2 is a diagrammatic view respectively in section showing the FIG. 1assembly;

FIG. 3 is a diagrammatic perspective view showing an assembly made inaccordance with another embodiment of the invention;

FIG. 4 is a diagrammatic perspective view showing a variant embodimentfor the bushing of FIG. 3;

FIG. 5 is a diagrammatic view respectively in section showing theassembly of FIG. 3;

FIG. 6 is a diagrammatic perspective view showing an assembly made inaccordance with another embodiment of the invention; and

FIG. 7 is a diagrammatic section view showing the FIG. 6 assembly.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention applies in general manner to any assembly betweenparts made of composite material using one or more fastener systems thatpresent a coefficient of thermal expansion greater than the coefficientof thermal expansion of the composite material parts, and in which thefastener system is to have no or very little impact on the aerodynamicperformance of the assembly.

The parts to be assembled together may in particular be made ofthermostructural ceramic matrix composite (CMC) material, i.e. anymaterial made up of reinforcement made of refractory fibers (carbonfibers or ceramic fibers) densified by a ceramic matrix that is alsorefractory, such as the following materials: C/SiC, SiC/SiC, C/C—SiC,etc. The parts may equally well be made out of other composite materialspresenting a low coefficient of expansion, such as C/C materials(reinforcement and matrix both made of carbon).

The assembly of the invention is particularly, but not exclusively, foruse in making all or part of aeroengine afterbody assemblies such asexhaust cones (also known as “plugs”), flaps for variable sectionnozzles, or aft pylon fairings (APFs).

FIGS. 1 and 2 show an assembly in accordance with an embodiment of theinvention. As shown in FIG. 1, an assembly 100 between two parts 10 and20, where the part 10 is made of thermostructural CMC material while thepart 20 is made of metal, is implemented by means of a fastener system50 comprising a screw 30, a nut 40, a bushing 60, a washer 70, and aspacer 80. More precisely, the screw 30 has a square head 31 from whichthere extends a shank 32 having a threaded portion 320 at its distalend. The nut 40 has tapping 43 for co-operating with the threadedportion 32 of the screw 30.

The bushing 60 has a collar 61 presenting an inside face 610 of squareshape matching the shape of the square head 31 of the screw 30, and anoutside face 611 of conical shape. The screw 30 and the nut 40 may bemade in particular out of any one of the following materials: Inconel®625 or 718, Waspaloy®, Haynes® 282®, A286 type stainless steel,titanium, TZM (Ti—Zr—Mo) alloy, or any other high performance steel.

As shown in FIG. 2, the collar 61 of the bushing 60 is received in acountersink 12 formed in the part 10, while the shank 32 of the screw 30passes through orifices 11 and 21 formed respectively in the parts 10and 20. Inside the bushing 60, the collar 61 defines an inside space 63that receives the screw 30. The square head 31 of the screw 30 isreceived in the collar 61 while a proximal portion of the shank 32 isreceived in an opening 64 formed in the bottom of the inside space 63 ofthe bushing 60. The parts 10 and 20 are assembled against each other bytightening the nut 40 on the threaded portion 320 of the shank 32 of thescrew 30, the spacer 80 being interposed between the nut 40 and the part20.

The square head 31 of the screw 30 bears against the inside face 610 ofthe collar 61 of the bushing 60, while the outside face 611 of thecollar 61 bears against the countersink 12 formed in the part 10. Theoutside face 611 of the collar 61 presents a cone angle β₆₁₁corresponding to the angle formed between the axis of revolution X₆₀ ofthe collar and the generator line G₆₁₁ of the outside face 611 of thecollar 61.

In accordance with the invention, by using a bushing having its collarwith an outside face that is conical in shape, the bearing area of thesquare head 31 of the screw 30 against the part 10 is increased. Thisincrease in bearing area makes it possible to reduce the crushingpressure and also the inter-lamination shear stress in the part 10 so asto increase the tightening force that can be applied between the parts10 and 20 without risk of damage, thereby increasing the capacity of theconnection for taking up force. In addition, since the screw/bushinginterface is decoupled from the interface with the part 10, it ispossible to use standard screws, i.e. screws that are easy andinexpensive to obtain.

By way of non-limiting example, the cone angle β₆₁₁ of the outside face611 of the collar may lie in the range 45° to 75°.

The material of the bushing 60 is selected for its coefficient ofthermal expansion, which is preferably greater than that of the screwand should serve to compensate in part for the difference in expansionbetween the composite material and the metal by means of “cone-on-cone”radial expansion that causes radial tension to be applied. The materialof the bushing 60 is also selected for its high temperaturecharacteristics. The bushing may in particular be made out of any one ofthe following materials: Inconel® 625 or 718, Waspaloy®, Haynes® 282®,A286 type stainless steel, titanium, TZM (Ti—Zr—Mo) alloy, or any otherhigh performance steel.

The spacer 80 serves to allow forces to transit between the nut 40 andthe part 20, while avoiding discontinuities of section modulus.Nevertheless, the fastener system 50 need not include the spacer 80, inwhich case the nut 40 would be in direct contact with the part 20. Thematerial of the spacer 80 is selected for its high temperaturecharacteristics and for its coefficient of thermal expansion, which ispreferably greater than that of the screw so as to take up in part thedifference of expansion between the composite material and the spacer.The spacer may in particular be made out of any one of the followingmaterials: Inconel® 625 or 718, Waspaloy®, Haynes® 282®, A286 typestainless steel, titanium, TZM (Ti—Zr—Mo) alloy, or any other highperformance steel.

The washer 70 serves to reserve a space between the parts 10 and 20 forassembling together in order to control the contact zone in terms ofshape, of size, and of surface state of the contact between the parts.The washer 70 may also have a function of compensating the tightening ofthe connection by making the washer of a suitable material such as, forexample: Inconel® 625 or 718, Waspaloy®, Haynes® 282®, A286 typestainless steel, titanium, TZM (Ti—Zr—Mo) alloy, or any other highperformance steel. The use of the washer 70 is optional in that thefastener system need not include the washer 70, with the parts 10 and 20then being in direct contact.

By acting as a guide for the screw 30 while tightening the nut 40, thebushing 60 can also serve to center the connection by adding acylindrical portion (not shown in FIGS. 1 and 2).

As shown in FIG. 2, it can be seen that beside the outside face 10 a ofthe part 10, the head 31 of the screw 30 is fully received in the collar61, which itself is fully received in the countersink 12, andconsequently the head of the screw together with the bushing have verylittle impact on the aerodynamics of the part 10 (the part has a planeor flush surface). In addition, when the assembly 100 is subjected tohigh temperatures, e.g. when it is immersed in a hot stream ofcombustion gas, the radial expansion of the collar 61 serves to maintaincontact with the countersink 12, in spite of the axial expansion of thescrew 30 (expulsion effect).

FIGS. 3 and 5 show an assembly in accordance with another embodiment ofthe invention. As shown in FIG. 3, an assembly 400 between two parts 310and 320, the part 310 being made of CMC material while the part 20 ismade of metal, is implemented by means of a fastener system 350comprising a screw 330, a nut 340, a bushing 360, a washer 370, and aspacer 380. More precisely, the screw 330 has a flat head 331 from whichthere extends a shank 332 having a threaded portion 3200 at its distalend. The nut 340 has tapping 343 for co-operating with the threadedportion 332 of the screw 330. The bushing 360 has a collar 361presenting an inside face 3610 and an outside face 3611, each of whichis conical in shape. In the presently-described example, the bushing 360also has a drum 362 extending from the collar 61. The drum 362 isoptional, it being possible for the bushing 360 to comprise only thecollar 361. The screw 330 and the nut 340 may in particular be made outof any one of the following materials: Inconel® 625 or 718, Waspaloy®,Haynes® 282®, A286 type stainless steel, titanium, TZM (Ti—Zr—Mo) alloy,or any other high performance steel.

As shown in FIG. 5, the collar 361 of the bushing 360 is received in acountersink 312 formed in the part 310, while the drum 362 passesthrough orifices 311 and 321 formed respectively in the parts 310 and320. The collar 361 and the drum 362 define an inside space 363 insidethe bushing 360 in which the screw 330 is received. The flat head 331 ofthe screw 330 is received in the collar 361, while a proximal portion ofthe shank 332 is received in the drum 362. The parts 310 and 320 areassembled against other by tightening the nut 340 on the threadedportion 3200 of the shank 332 of the screw 330, the spacer 380 beinginterposed between the nut 340 and the part 320.

The flat head 331 of the screw 330 bears against the inside face 3610 ofthe collar 361 of the bushing 360, while the outside face 3611 of thecollar 361 bears against the countersink 312 formed in the part 310. Theoutside face 3611 of the collar 361 presents a cone angle β₃₆₁₁ that isgreater than the cone angle α₃₆₁₀ presented by the inside face 3610 ofsaid collar. The cone angles β₃₆₁₁ and α₃₆₁₁ correspond to the angleformed between the axis of revolution X₃₆₀ of the collar and therespective generator lines G₃₆₁₀ and G₃₆₁₁ of the inside and outsidefaces 3610 and 3611 of the collar 361.

In accordance with the invention, by using a bushing having its collarwith an outside face of cone angle and diameter greater than the coneangle and diameter of its inside face, the bearing area of the screwhead against the part 310 is increased. This increase in bearing areamakes it possible to reduce the crushing pressure and also theinter-lamination shear stress in the part 310 so as to increase thetightening force between the parts 310 and 320 without risk of damage,thereby increasing the capacity of the connection for taking up force.In addition, since the screw/bushing interface is decoupled from theinterface with the part 310, it is possible to use standard screws, i.e.screws that are easy and inexpensive to obtain, since the cone angleα₃₆₁₀ presented by the inside face 3610 can match the cone angle ofstandard screws without any impact on the connection.

By way of non-limiting example, the cone angle α₃₆₁₀ of the inside face3610 of the collar 361 may lie in the range 30° to 60°, while the coneangle β₃₆₁₁ of the outside face 3611 of the collar may lie in the range45° to 75°.

The material of the bushing 360 is selected for its high temperaturecharacteristics and for its coefficient of thermal expansion, which ispreferably greater than that of the screw and should serve to compensatein part for the difference in expansion between the composite materialand the metal by means of “cone-on-cone” radial expansion that causesradial tension to be applied. The bushing may in particular be made ofany one of the following materials: Inconel® 625 or 718, Waspaloy®,Haynes® 282®, A286 type stainless steel, titanium, TZM (Ti—Zr—Mo) alloy,or any other high performance steel.

The spacer 380 serves to cause forces to transit between the nut 340 andthe part 320, while avoiding any discontinuities of section modulus.Nevertheless, the fastener system 350 need not include the spacer 380,in which case the nut 340 would be in direct contact with the part 320.The material of the spacer 380 is selected for its high temperaturecharacteristics and for its coefficient of thermal expansion, which ispreferably greater than that of the screw so as to take up in part thedifference of expansion between the composite material and the spacer.The spacer may in particular be made out of any one of the followingmaterials: Inconel® 625 or 718, Waspaloy®, Haynes® 282®, A286 typestainless steel, titanium, TZM (Ti—Zr—Mo) alloy, or any other highperformance steel.

The washer 370 serves to reserve a space between the parts 310 and 320for assembling together in order to control the contact zone in terms ofshape, of size, and of surface state of the contact between the parts.The washer 70 may also have a function of compensating the tightening ofthe connection by making the washer out of a suitable material such as,for example: Inconel® 625 or 718, Waspaloy®, Haynes® 282®, A286 typestainless steel, titanium, TZM (Ti—Zr—Mo) alloy, or any other highperformance steel.

The use of the washer 70 is optional in that the fastener system neednot include the washer 70, with the parts 10 and 20 then being in directcontact.

By acting as a guide for the screw 30 while tightening the nut 40, thebushing 60 can also serve to center the connection when it is providedwith a cylindrical portion such as the drum 362.

In the variant embodiment shown in FIG. 4, the fastener system of theinvention may include a bushing 90 with its drum 92 locatedeccentrically relative to its collar 91. Such a bushing serves to takeup clearance during tightening with screws having shanks that are not inaxial alignment with their screw heads.

As shown in FIG. 5, it can be seen that beside the outside face 310 a ofthe part 310, the head 331 of the screw 330 is fully received in thecollar 361, which is itself fully received in the countersink 312, andconsequently the head of the screw and the bushing have very littleimpact on the aerodynamics of the part 310 (the part has a plane orflush surface). In addition, when the assembly 400 is subjected to hightemperatures, e.g. when it is immersed in a hot stream of combustiongas, the radial expansion of the collar 361 serves to maintain contactwith the countersink 312, with this applying in spite of the axialexpansion of the screw 330 (expulsion effect).

FIGS. 6 and 7 show an assembly in accordance with another embodiment ofthe invention. As shown in FIG. 6, an assembly 200 between two parts 110and 120, the part 110 being made of CMC material while the part 120 ismade of metal, is implemented by means of a fastener system 150comprising a rivet 130, a first washer 140, a bushing 160, a secondwasher 170, and a spacer 180. More precisely, the rivet 130 has a flathead 131 from which there extends a shank 132. The washer 140 has acentral opening 141 for receiving the free end 1320 of the shank 132.The washer 140 also has both a plane first face 142 that is to bepressed against the spacer 180 or the outside surface 120 a of thesecond part 120 if there is no spacer 180, and also a second face 143.The central opening 141 in the washer 140 includes a countersink 1410.The rivet 130 and the washer 140 may in particular be made out of anyone of the following materials: Inconel® 725 or 718, Waspaloy®, Haynes®282®, A286 type stainless steel, titanium, TZM (Ti—Zr—Mo) alloy, or anyother high performance steel.

As shown in FIG. 7, the collar 161 of the bushing 160 is received in acountersink 112 formed in the part 110, while the drum 162 passesthrough orifices 111 and 121 formed respectively in the parts 110 and120. The collar 161 and the drum 162 define an inside space 163 insidethe bushing 160 in which the rivet 130 is received. The flat head 131 ofthe rivet 130 is received in the collar 161, while a proximal portion ofthe shank 132 is received in the drum 162. The free end 1320, whichincludes a central recess 1321, is enlarged by flattening so as to pressthe edges of the end 1320 against the countersink 1410 of the centralopening 141 in the washer 140. The free end may be enlarged either whenhot or when cold, depending on the material constituting the rivet, andby using a riveting head. The two parts 110 and 120 are then securedtogether by riveting. The rivet 130 could be replaced by a blind rivet(of the lock-bolt type).

The flat head 131 of the rivet 130 bears against the inside face 1610 ofthe collar 161 of the bushing 160, while the outside face 1611 of thecollar 161 bears against the countersink 112 formed in the part 110. Theoutside face 1611 of the collar 161 presents a cone angle β₁₆₁₁ and adiameter that are greater than the cone angle α₁₆₁₀ and the diameterpresented by the inside face 1610 of said collar. The cone angles β₁₆₁₁and α₁₆₁₀ correspond to the angle formed between the axis of revolutionX₁₆₀ of the collar and the respective generator lines G₁₆₁₀ and G₁₆₁₁ ofthe inside and outside faces 1610 and 1611 of the collar 161.

In accordance with the invention, by using a bushing with its collarhaving an outside face with a cone angle and a diameter that are greaterthan the cone angle and the diameter of its inside face, the bearingarea of the head of the rivet against the part 110 is increased. Thisincrease in bearing area makes it possible to reduce the crushingpressure and also the inter-lamination shear stress in the part 110 soas to increase the tightening force between the parts 110 and 120without risk of damage, thereby increasing the capacity of theconnection for taking up force.

By way of non-limiting example, the cone angle α₁₆₁₀ of the inside face1610 of the collar 161 may lie in the range 30° to 60°, while the coneangle β₁₆₁₁ of the outside face 1611 of the collar may lie in the range45° to 75°.

The material of the bushing 160 is selected for its high temperaturecharacteristics and for its coefficient of thermal expansion, which ispreferably greater than that of the screw and should serve to compensatein part for the difference in expansion between the composite materialand the metal by means of “cone-on-cone” radial expansion that causesradial tension to be applied. The bushing may in particular be made outof any one of the following materials: Inconel® 725 or 718, Waspaloy®,Haynes® 282®, A286 type stainless steel, titanium, TZM (Ti—Zr—Mo) alloy,or any other high performance steel.

The spacer 180 serves to cause forces to transit between the washer 140and the part 120, while avoiding any discontinuities in section modulus.Nevertheless, the fastener system 150 need not include the spacer 180,in which case the washer 140 would be in direct contact with the part120. The material of the spacer 180 is selected for its high temperaturecharacteristics and for its coefficient of thermal expansion, which ispreferably greater than that of the screw so as to take up part of thedifference of expansion between the composite material and the spacer.The spacer may in particular be made out of any one of the followingmaterials: Inconel® 725 or 718, Waspaloy®, Haynes® 282®, A286 typestainless steel, titanium, TZM (Ti—Zr—Mo) alloy, or any other highperformance steel.

The second washer 170 serves to reserve a space between the parts 110and 120 for assembling together in order to control the contact zone interms of shape, of size, and of surface state of the contact between theparts. The washer 170 may also have a function of compensating thetightening of the connection by making the washer out of a suitablematerial, such as for example: Inconel® 625 or 718, Waspaloy®, Haynes®282®, A286 type stainless steel, titanium, TZM (Ti—Zr—Mo) alloy, or anyother high performance steel. The use of the washer 170 is optional inthat the fastener system need not include the washer 170, with the parts110 and 120 then being in direct contact.

As shown in FIG. 7, it can be seen that beside the outside face 110 a ofthe part 110, the head 131 of the rivet 130 is fully received in thecollar 161, which is itself fully received in the countersink 112, andconsequently the head of the rivet and the bushing have very littleimpact on the aerodynamics of the part 110 (the part has a plane orflush surface). In addition, when the assembly 200 is subjected to hightemperatures, e.g. when it is immersed in a hot stream of combustiongas, the radial expansion of the collar 161 serves to maintain contactwith the countersink 112, with this applying in spite of the axialexpansion of the rivet 130. A similar compensation effect takes place atthe enlarged end portion 1320 of the rivet 130 in contact with thecountersink 1410 in the opening 141 of the washer 140.

The invention claimed is:
 1. An assembly comprising a first part made ofcomposite material and a second part, which first and second parts areheld one against the other by at least one fastener system having afastener element with a head from which there extends a shank, thefastener system also having a bushing, said bushing including a collarpresenting an inside face and an outside face of conical shape, the headof the fastener element bearing against the inside face of the collar,while the outside face of the collar bears against a countersink formedin the first part, wherein the fastener system comprises a rivet havinga flat head from which there extends a shank having an enlarged end anda first washer including a central countersink against the surface ofwhich the enlarged end of the shank of the rivet rests, the collar ofthe bushing presenting an inside face of conical shape receiving theflat head of the rivet, and wherein the outside face of the collarpresents a cone angle that is greater than the cone angle of the insideface of said collar, wherein the fastener system further comprises aflat washer interposed between the facing faces of the first and secondparts, wherein the bushing has a drum that extends through said flatwasher, and wherein the second part is made of composite material.
 2. Anassembly according to claim 1, wherein the fastener system furthercomprises a spacer interposed between the second part and the firstwasher.
 3. An assembly according to claim 2, wherein the spacer presentsa coefficient of thermal expansion that is greater than the coefficientof thermal expansion of the rivet.
 4. An assembly according to claim 1,wherein each of the first and second parts presents a thickness of lessthan 3 mm.
 5. An assembly according to claim 1, wherein the first andsecond parts are aeroengine afterbody parts or aerodynamic fairing partsof an aft pylon fairing.